The company that produces Boob Job cream has been accused of being a "charlatan and a bully" for using libel laws to silence a plastic surgeon who criticised its product.

Rodial, which claims its cosmetic cream can increase a woman's breast size by up to 8%, threatened to sue Dalia Nield after she said the product's claim was "highly unlikely".

Nield is being represented by Robert Dougans, the lawyer who also acted for science writer Simon Singh after he faced a similar libel for comments he wrote about the British Chiropractic Association.

But speaking in the house of commons yesterday, Conservative MP David Davis said that the ability of companies such as Rodial to use libel law against critics was a violation of ancient principles of English law.

"[Rodial's threat] would be ludicrous, bordering on the farcical, were it not so serious in its wider implications," said Davis.

"It is a disgraceful tactic, and it should not be possible under a decently balanced judicial system."

The debate on libel reform represents the latest use by MPs of parliamentary privilege to bypass the threat of a lawsuit for speaking out about individual cases.

Last year Labour MP Paul Farrelly asked a question to the then justice secretary, Jack Straw, revealing the injunction obtained by toxic waste company Trafigura, after the Guardian was banned from reporting its existence.

"We have failed to defend one of our nation's primary virtues, free speech," said Davis. "We have also failed in another duty, that of protecting the weak and vulnerable from the rich and powerful."

"Time and again we are seeing commercial companies doing this to silence critics," Davis added. "Using the law to silence legitimate criticism is to put shareholder interest above public health, and sometimes, above public safety."

The debate comes as the government continues to review libel law and has promised a new bill early next year.

Yesterday, the supreme court made significant changes to the defence of "fair comment", invoked by defendants in libel cases to show their criticisms are honestly-held views based on fact.